This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Original Description: The aim of this project is to develop a specific 14C-postlabelling assay to detect very low levels of a particular type of DNA adduct, O6-methyl deoxyguanosine (O6-MedG). This adduct is one of the less abundant lesions formed by alkylating carcinogens, has been detected at levels of 1 adduct/10^8 nucleotides by 32P-postlabelling and is known to be mutagenic, recombinogenic and cytotoxic. O6-MedG is formed as a consequence of exposure to methylating agents, nitrosamines present in tobacco smoke, and nitrate treated foods. This assay will therefore provide a valuable tool for the detection of low levels of O6-MedG adducts in human populations exposed to such alkylating adducts.